A common feature of all saw chains used in present day motor saws and like forest clearing machines is that they comprise various types of links. Those links which need to be sharpened or ground are referred to as cutter links and are found in two mutually different configurations, namely right hand and left hand link configurations. In order to achieve an optimum cutting ability or effect, the toothed cutters of these cutter links must be ground with the setting of the grinding machine adjusted to the type of link to be ground. Seated forwardly of the cutting tooth of both link configurations is an extra tooth or depth gauge. Although it is sometimes necessary to adjust the length of this extra tooth, it is not normally ground at the same time as the cutting teeth, and neither should it be confused with a cutting tooth by the sensing or detecting devices of automatic saw chain grinders. The cutter links of a saw chain are normally separated by a spacing link or drive link, such that each alternate cutter link is a right hand link and each other cutter link is a left hand link. The majority of automatic saw chain grinders are constructed to grind each alternate cutter link, e.g. the right hand links, with the grinding wheel in a first setting, and then to grind the intermediate links, i.e. the left hand links, with the grinding wheel in a second setting. However, when joining together the ends of saw chains, e.g. after having adjusted the lengths thereof, it is very usual to use two identical cutter link configurations, i.e. links of the same kind, side by side, which causes problems when grinding such chains in automatic grinders. Exceptions are to be found in which forward feeding of the chain is monitored by some form of detector means or the other which when detecting the presence of two mutually sequential cutter teeth of the same kind will cause the machine to stop and therewith enable the machinist to move the irregularly placed cutter links manually past the grinding location. In this case the grinder cannot be said to be fully automatic.
In the case of automatic saw chain grinders, the saw chain normally passes over a chain support which includes horizontally extending support or guide plates which are delimited in the direction of the longitudinal axes by support wheels from which the chain hangs in a loop and is passed around a drive or support wheel, intended for tensioning the chain. The drive wheels may be driven by an electric motor over a friction clutch, and the motor may be controlled by a programmed mechanism to advance the saw chain through a distance corresponding substantially to the distance between two cutter links which face in mutually the same direction, and then to move the chain in reverse until a cutter link to be ground is positioned in a grinding location, defined by a stop means, whereafter the link is locked securely for grinding purposes. In other known kinds of automatic saw chain grinders, the saw chain is advanced through the agency of a plate which is driven by a camming plate and which imparts a reciprocating movement to the chain support, wherewith a feed finger arranged on the plate grips and feeds an appropriate chain link to a grinding location, where the link is located firmly for grinding purposes.
Both of the aforedescribed saw-chain feeding methods have the earlier mentioned drawback of not being devised for differentiating between right hand and left hand links. Furthermore, the programmed mechanisms are normally programmed to accommodate and grind links of the longest length that can possibly occur, which extends the length of the chain feed movements unnecessarily. Another drawback with known saw chain grinders is that they lack means which will ascertain that the cutter link remains constantly in position for grinding during the grinding process. Those detecting devices provided on certain types of known grinding machines for checking that the cutter link is located in the correct grinding position must be swung to one side during the grinding process, so as not to be damaged by the grinding wheel.